This disclosure relates to composites having tunable dielectric constants, methods of manufacture thereof, and articles comprising the same.
The permittivity of ferroelectric materials is dependent upon the voltage at which it is measured. This voltage dependency makes the ferroelectric material potentially useful for tunable devices that operate at microwave frequencies. However, in order to function well at microwave frequencies, it is desirable for the ferroelectric materials to have low dielectric losses. In order to match the reactance of a varistor (that comprises a ferroelectric material) to the impedance of the rest of the circuit, it is desirable for the capacitance value of the ferroelectric material to be low at the microwave frequencies. The currently available ferroelectric materials however, all exhibit a very high capacitance value (i.e., they have high dielectric constants of greater than or equal to about 100).
In order to function successfully in high frequency applications (e.g., radio frequencies, microwave frequencies or higher), it is desirable to use materials that have a dielectric constant of less than or equal to 100. It is further desirable that these materials be tunable and have low dielectric losses in the radio frequency or microwave frequency range. A tunable material is one whose dielectric constant can be varied with frequency or with voltage. While there exist some low dielectric constant materials for radio frequency and microwave applications, these materials are not tunable. Other ferroelectric materials such as, for example, CaCu3Ti4O12 are tunable over a broad frequency range but have high dielectric losses in their ceramic bulk state.
Materials that have a low capacitance value (e.g., a low dielectric constant) and that can be tuned directly by frequency or by an electrical field are not known. It is therefore desirable to manufacture materials that have a low dielectric constant and whose dielectric constants are capable of being tuned.